Nortel Optical Multiservice Edge 6130, Planning Manual, Page: 289 / 292

Appendix A: Data communications planning 10-103
Planning Guide NT6Q92MA Rel 1.0 Iss 1 Standard September 2006
routing protocols (for example, RIP). A static route should be assigned a high
preference and a default route a low one.
Static and default routes
Static routes are manually configured on a router in contrast to routes learned
via a routing protocol. Static routes are permanent and remain in the routing
table even though an interface associated with the route goes down. They are
most commonly used for:
• Defining routes to use when two autonomous systems must exchange
routing information, rather than having entire routing tables exchanged.
Often subnetworks linked to a corporate network do not wish to receive
routing updates but require some facilities provided by the corporate
network. The intermediate router on the border would advertise to the
corporate network that it had a route to the subnetwork.
• A network which has dial-on-demand links. Routing updates passing over
this link would keep the link up permanently. A static route ensures that the
link is only enabled when traffic data requires the link to reach its
destination.
Routers must be configured to listen to and redistribute static routes.
Default routes are a form of static routes in that they provide a catch-all for
destinations not contained in routing tables. In effect they provide a static
route to a large network rather than a specific IP address or subnetwork. In the
case of the subnetwork attached to a corporate network, the intermediate
router on the border has a default route to the corporate network advertised
into the subnetwork.
Figure 10-30 shows an example of the way that static routes and default
routes are used.
Figure 10-30
Default and static routes
Intermediate router
Subnetwork
Corporate Network
default route to
corporate network
static route
to subnetwork
route advertisement
route advertisement
47.132.32.0/20
(0.0.0.0 mask 0.0.0.0)
(47.132.32.0 mask 255.255.240.0)
and Internet gateway